The very first unit you will encounter in the Lusitanian roster, the Ibaranta, is in fact a levy spear unit that actually functions more as a medium infantryman that can be cloaked. Although it's not as strong as say, Roman Cohors or Celtic Neitos, what makes it such a useful unit lies in three areas. The first and nost obvious ability of the Ibaranta is to remain hidden. Pack this with its availability and its ability to cause decent damage (despite being a levy unit) and you have a powerful infantry force ideal for sneak attacks on unsuspecting enemies. While the Celtiberian Caetranann are meant to be used in a more passive manner with regards to their cloaking ability, the ability of the Ibaranta to remain unseen everywhere it goes makes it an ideal unit for raiding, In large numbers, the Ibaranta can be deadly if used to raid and attack enemy settlements which are unprotected and if the player failed to set up attrition fields or intelligence gathering to check their advance. Ibaranta while fast on foot are not as fast as some light infantrymen (let alone cavalry) and if you face dedicated units such as sword infantry like the British Kluddobro , you are best advised to flee or seek more support.
History
The terrain of Iberia which varied between arid deserts and deadly mountain passes meant that whatever military cultures in that area had to be as flexible and innovative as possible. Light infantry and skirmisher cavalry were ideal for the terrain of the Iberian peninsula, making use of hills, valleys and broken terrain to function as strong points for cover and refuge when not engaging in the intertribal raiding which characterised pre-Roman society (as well as post-Roman society throughout the Middle Ages).
Although the Celtiberians were proficient in metalworking and could craft swords which would be the envy of the Roman world, the most common weapon in use was the spear. Fairly simple yet effective in skilled hands, spears were weapons ideal for a society that had to be self-sufficient and seasoned in order to survive. Herding, the main economic activity of the Iberian tribes, was an activity fraught with many dangers, particularly from one's peers and shepherds who survived long enough would become warriors, fit to serve the tribal chiefs who were obliged to fight in the defence of those who swore fealty to them. Thus in times of war, the Iberian tribal chiefs could be assured of being capable of raising a good many spearmen from levying the pastoral classes.